/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.channel.nio;

import io.netty.channel.*;

import java.io.IOException;
import java.net.PortUnreachableException;
import java.nio.channels.SelectableChannel;
import java.nio.channels.SelectionKey;
import java.util.ArrayList;
import java.util.List;

/**
 * {@link AbstractNioChannel} base class for {@link Channel}s that operate on messages.
 */
public abstract class AbstractNioMessageChannel extends AbstractNioChannel {
  boolean inputShutdown;
  
  /**
   * @see AbstractNioChannel#AbstractNioChannel(Channel, SelectableChannel, int)
   */
  protected AbstractNioMessageChannel(Channel parent, SelectableChannel ch, int readInterestOp) {
    super(parent, ch, readInterestOp);
  }
  
  @Override
  protected AbstractNioUnsafe newUnsafe() {
    return new NioMessageUnsafe();
  }
  
  @Override
  protected void doBeginRead() throws Exception {
    if (inputShutdown) {
      return;
    }
    super.doBeginRead();
  }
  
  private final class NioMessageUnsafe extends AbstractNioUnsafe {
    
    private final List<Object> readBuf = new ArrayList<Object>();
    
    @Override
    public void read() {
      assert eventLoop().inEventLoop();
      final ChannelConfig config = config();
      final ChannelPipeline pipeline = pipeline();
      final RecvByteBufAllocator.Handle allocHandle = unsafe().recvBufAllocHandle();
      allocHandle.reset(config);
      
      boolean closed = false;
      Throwable exception = null;
      try {
        try {
          do {
            int localRead = doReadMessages(readBuf);
            if (localRead == 0) {
              break;
            }
            if (localRead < 0) {
              closed = true;
              break;
            }
            
            allocHandle.incMessagesRead(localRead);
          } while (allocHandle.continueReading());
        } catch (Throwable t) {
          exception = t;
        }
        
        int size = readBuf.size();
        for (int i = 0; i < size; i++) {
          readPending = false;
          // todo 读触发之后  开始触发 pipeline()
          pipeline.fireChannelRead(readBuf.get(i));
        }
        readBuf.clear();
        allocHandle.readComplete();
        // pipeline 完成
        pipeline.fireChannelReadComplete();
        
        if (exception != null) {
          closed = closeOnReadError(exception);
          
          pipeline.fireExceptionCaught(exception);
        }
        
        if (closed) {
          inputShutdown = true;
          if (isOpen()) {
            close(voidPromise());
          }
        }
      } finally {
        // Check if there is a readPending which was not processed yet.
        // This could be for two reasons:
        // * The user called Channel.read() or ChannelHandlerContext.read() in channelRead(...) method
        // * The user called Channel.read() or ChannelHandlerContext.read() in channelReadComplete(...) method
        //
        // See https://github.com/netty/netty/issues/2254
        if (!readPending && !config.isAutoRead()) {
          removeReadOp();
        }
      }
    }
  }
  
  @Override
  protected void doWrite(ChannelOutboundBuffer in) throws Exception {
    final SelectionKey key = selectionKey();
    final int interestOps = key.interestOps();
    
    for (; ; ) {
      Object msg = in.current();
      if (msg == null) {
        // Wrote all messages.
        if ((interestOps & SelectionKey.OP_WRITE) != 0) {
          key.interestOps(interestOps & ~SelectionKey.OP_WRITE);
        }
        break;
      }
      try {
        boolean done = false;
        for (int i = config().getWriteSpinCount() - 1; i >= 0; i--) {
          if (doWriteMessage(msg, in)) {
            done = true;
            break;
          }
        }
        
        if (done) {
          in.remove();
        } else {
          // Did not write all messages.
          if ((interestOps & SelectionKey.OP_WRITE) == 0) {
            key.interestOps(interestOps | SelectionKey.OP_WRITE);
          }
          break;
        }
      } catch (Exception e) {
        if (continueOnWriteError()) {
          in.remove(e);
        } else {
          throw e;
        }
      }
    }
  }
  
  /**
   * Returns {@code true} if we should continue the write loop on a write error.
   */
  protected boolean continueOnWriteError() {
    return false;
  }
  
  protected boolean closeOnReadError(Throwable cause) {
    if (!isActive()) {
      // If the channel is not active anymore for whatever reason we should not try to continue reading.
      return true;
    }
    if (cause instanceof PortUnreachableException) {
      return false;
    }
    if (cause instanceof IOException) {
      // ServerChannel should not be closed even on IOException because it can often continue
      // accepting incoming connections. (e.g. too many open files)
      return !(this instanceof ServerChannel);
    }
    return true;
  }
  
  /**
   * Read messages into the given array and return the amount which was read.
   */
  protected abstract int doReadMessages(List<Object> buf) throws Exception;
  
  /**
   * Write a message to the underlying {@link java.nio.channels.Channel}.
   *
   * @return {@code true} if and only if the message has been written
   */
  protected abstract boolean doWriteMessage(Object msg, ChannelOutboundBuffer in) throws Exception;
}
